Measuring time, temperature, mass and volume

Chemistry results are useful only when another person can understand and repeat the measurements. Choose suitable apparatus, record the value with justified precision and always include its unit.

What the skill involves

Measurement is the process of assigning a numerical value and unit to a quantity (e.g., time, temperature, mass, volume) using an appropriate instrument.

What you need to know

• In school chemistry, common units are second (s), degree Celsius (°C), gram (g), cm³ and dm³.
• Choose the instrument based on the required resolution (the smallest readable change), the required accuracy, and the job (fixed volume vs variable volume).
• Precision describes how close repeated readings are to one another; it is not the same as resolution.
• Record readings to the correct decimal places and include units.
• Reduce errors: read scales at eye level to avoid parallax error, and read the correct part of the meniscus.

Putting the skill into practice

Measurement of time

• SI unit: second (s).
• Common instrument: stopwatch.

Measurement of temperature

• Record laboratory temperature in degrees Celsius (°C) unless the question specifies another unit.

• Instruments: laboratory thermometer, digital thermometer, data logger (temperature sensor + automatic recording).

• Good practice: ensure the bulb/sensor is fully in the substance and not touching the container wall; allow the sensor to respond before taking a steady-temperature reading. If the temperature is changing, take repeated readings or use a data logger so you can identify the maximum or minimum.

Measurement of mass

• SI unit: kilogram (kg). In school labs, mass is usually recorded in gram (g).
• Instruments: beam balance (rare) and electronic balance.

• When measuring a substance directly in a container, tare (zero) the balance with the empty container before adding the substance. In a weigh-by-difference method, record the required masses instead of taring between readings.

Measurement of volume (liquids)

• SI unit: cubic metre (m³). In chemistry you commonly use cm³ and dm³ (L).
• Key conversions:
  • 1 cm³ = 1 mL
  • 1 dm³ = 1 L = 1000 cm³
  • 1000 L = 1 m³

The apparatus you choose depends on whether you need an approximate volume or a carefully measured volume, and whether you are transferring liquid or preparing a solution.

Match the apparatus to the job:

• Transfer 25.0 cm³ accurately → volumetric pipette.
• Measure about 25 cm³ → measuring cylinder.

A question may call a pipetted volume “exact”. This means using suitable calibrated apparatus; every real measurement still has some uncertainty. A standard burette graduated every 0.1 cm³ is normally read to the nearest 0.05 cm³ for this course.

For measuring the volume of gases, see Collection of Gases and Measurement of their Volumes.

Meniscus and parallax error

When a liquid is in a narrow container (measuring cylinder, burette, pipette), the surface is usually curved. This curved surface is the meniscus.

• Concave meniscus (e.g., water): read the bottom of the curve.
• Convex meniscus (e.g., mercury): read the top of the curve.
• Read at eye level to avoid parallax error (apparent shift in reading when viewed from above/below the scale).

Avoiding common mistakes

• Writing “accurate to 0.01” when you mean the resolution is 0.01.
• Forgetting to tare the balance before measuring mass in a container.
• Reading the meniscus from above/below eye level (parallax).
• Recording a burette reading to 1 decimal place, or using a final digit other than 0 or 5 for the nearest-0.05 cm³ reading.
• Using a measuring cylinder or beaker when the question says “exactly 25.0 cm³”.

Explaining your method

Worked examples

Try it independently

Practise and check